Structural tower



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L. A. PRESCOTT ET AL STRUCTURAL TOWER Filed March 5, 1925 2 Sheets-Shen 1 i fm .1

Aug. 25, 1925.

' L. A. PRESCOTT ET AL STRUCTURAL TOWER Filed March 5, 1925 2 Sheets-Shut INVENTCRS ML; La/25,

lim.- ITT 6, ,y u@ v n E F 4, 3 J 7 I E- r Patented Aug. 25, 1925.

UNITED ASTATES PATENT OFFICE.

LYLE A. PRESCOTT AND IRA W. MARSHALL, OF PITTSBURGH, PENNSYLVANIA, AS-

SIGNORS TO BLAW-KNOX COMPANY, 0F PITTSBURGH, PENNSYLVANIA, A. C0331-i .PORATION 0F NEW JERSEY.

STRUCTURAL TOWER.

',f r j' Y Application filed March 3, 1925. Serial No. 12,813.

To all whom t may concern:

Be it known that we, LYLE A. PREsco'rT and IRA W. MARSHALL, citizens of the United States, residing at Pittsburgh, county of Allegheny, and State of Pennsylvania, have invented a new and useful Improvement in Structural Towers, of which the following is a full, clear, and exact description.

The present invention relates to structural towers, such as are employed for carrying transmission lines, telegraph and telephone wires, and more particularly to the construction of the cross arms which carry the transmission wires.

The object of the invention is to reduce the stresses in a tower to which it would be subjected when one or more of the transmission wires supported by the tower breaks, as they may do from excess wind or ice loads or other causes. At the present time it is customary to attach the conductors of a transmission line to the ends of the cross arms of the towers, and if one of the wires breaks in one of the adjoining spans, the pull of the wire in the other adjoining span caused by the weight of the wire and any ice or wind load that may be on it is transmitted back through the cross arm and the tower to the ground. This pull being at the end of the cross arm and away from the center of gravity of the tower, causes a torque or twisting moment on the tower and the members composing same must be strong enough to resist the resulting stresses. The web members which resist the torque stresses, as well as the cross arms, must, therefore, be much heavier than they would be were this torque or twisting moment absent.

By the present invention we propose to eliminate the twisting moment on the tower in large part by having each conductor attached to a member which, when the broken wire load comes upon it, will swing around into the direction of the line.

In the drawings:

Figure l is a side elevation of a portion of a tower of the usual corner post construction having our invention embodied therein.

Figure 2 is a sectional plan view on the line II-II of Figure l.

Figure 8 is a side elevation similar to Figure l showing our invention embodied in a tower of the type in which the usual corner posts are omitted, such as illustrated in Marshall Patent No. 1,506,984, granted September 2, 1924; and

Figure 4 is a sectional plan view on the line IV-IV of Figure 3.

Referring to the embodiment of the invention illustrated in Figures l and 2, T designates the tower and 2 one of its cross arms. Numeral 3 designates one of the transmission wires which is carried by insulators 4 suspended at the point 5 from the lower end of an angle member 6. The member 6 is secured at its upper end to the tower by a pivotal connection 7 which will permit the member to swing around into the direction in which the transmission wire is pulling. Member 6 is connected to the outer end ofthe cross arm by an easily breakable connection, such as the small bolt 8. The bolt 8 is intended merely to hold 75 the member attached to the cross arm only so long as the wire remains unbroken and normally receives little if any stress. In case the transmission wire breaks, however, the pull of the wire in the adjoining span will put sufficient stress on the connection to break it, allowing the member 6 to swing into the direction of the line. It is herein contemplated that the connection 8 will be made so that it will fail at a small load, and it need not be a bolt as shown, but may be any equivalent means which will hold the member in place under light loads and will give way under the heavier load imposed thereon when the wire breaks. Cross arm 2 must be strong enough to carry any stresses put into it by the connection 8, but need not be nearly as strong as cross arms are ordinarily made.

The pull or tension in a conductor hanging between two supports varies with the sag of the conductor which is the vertical distance from the elevation of the supports to the lowest point of the wire. As the length of the wire between two fixed supports is increased the sag also increases, and as it increases the tension in the wire decreases. With the wire supported at point 5 as shown in Figure l, the tension in the wire would be a certain amount depending upon theamount of the sag in the conductor. When the connection at point 8 fails and member (i swings into the direction of the line, the length of the member G is added to the length of the conductor wire. rllhis increased length increases the also and the pull in the conductor is greatly decreased, so that, with our arrangement not only are the torque or twisting moment stresses on the tower greatly reduced, but also the actual pull in the conductor is greatly reduced. The tower members, therefore, can be made much lighter and a great saving in the amount of steel required can be eii'ectod through the use of this arrangement.

The member G extending past the point 8 to the point 5 makes the point of support of the insulators below t-he member 2. This allows more clearance between the conductor wire 8 and the cross arm 2 when the conductor is swung over to the position 9, than would be the case where the insulators hung from the cross arm in the ordinary manner. It is very desirable to have this additional clearance, especially for the higher voltages, and at the present time this clearance is sometimes obtained by the use of a bracket extending down from the end oi5 the cross arm or an additional link is inserted between the cross arm and the top or the in sulators. Our arrangement does away with' the need of a bracket or additional link. The member 6, of course, does not have to be an angle and it may be more desirable to use some other shape for this member.

Figures 3 and t show the invention adapted to that type of tower having the corner posts omitted, as illustrated in the patent above referred to. rEhe cross arm 10 in this type of construction is connected to the members 11 at the corners of the tower which connect the upper ends or the diagonals oit one tower section to the lower ends ot the diagonals of the tower section next above. The conductor carrying member 6 is connected at its upper end to a transverse member made up of two spaced parallel angle members 12 connected to the two diagonals 13 at each of two opposite sides ont the tower where such diagonals cross each other. Brackets 14: are connected tothe ends et the parallel members 12 and the members G are pivoted at their upper ends to these bracket members. Otherwise, Athe construction is the same as illustrated in Figures 1 and 2.

lfhile we have shown and described certain preferred embodiments oi our invention, it will be understood that the invention is not limited to its illustrated embodiments but may be otherwise embodied within the scope ot the appended claims.

lWe claim:

1. ln a structural tower, a transmission wire, and means carried by said tower and.

extending at substantially right angles to the direction oit said wire for supporting the latter, said means being adapted to swing around into the direction oit said wire under the pull of said wire in an adjoining span when said wire in the other adjoining span breaks, substantially as described.

2. In a structural tower, a transmission wire, means carried by said tower and eX- tending` at an angle to the direction of said wire for supporting the latter, and a connection between said means and said tower adapted to break under the load imposed upon said connection by said wire in one adjoining span when said wire in the other adjoining span breaks, whereby said means is adapted to swing around into the direction o'j the wire, substantially as described.

3. A structural tower, comprising a cross arm, a member pivotally connected at its inner end to said tower and supported adjacent its outer end by said cross arm, a transmission wire attached to the outer end of said member, said member normally eX- tending in a direction transverse to the direction of said wire, and a connection between said member and cross arm adapted to break under the load imposed on said connection by said wire in one adjoining span when the wire breaks in the other adjoining span, whereby said member is adapted to swing into the direction of the wire, substantially as described.

In a structural tower, a horizontal cross arm, an inclined member pivotally connected at its inner end tok said tower at a point above said cross arm and having its outer end in position below said cross arm, a transmission wire attached to the outer end ot said arm, and means connecting said member to said cross arm adapted to break under the load imposed on said connecting means by said wire in one adjoining spa-n when the wire breaks in the other adj oining span, whereby said member is adapted to swing into the direction of the wire, substantially as described.

5. In a structural tower, a. transmission wire, an arm extending outwardly from said tower and having said wire connected thereto, a support for said arm, and a` connection between said support and said arm adapted to break under the load imposed on said connection by said wire in one adjoining span when the wire breaks in the other adjoining span, whereby said arm is adapted to swing into the direction of the wire, substantially as described.

In testimony whereof we have hereunto set our hands.

L. A. PRESCOTT. IRA YV. lVQARSl-lALL. 

